This invention relates to high-temperature, secondary electrochemical cells and batteries of such cells than can be employed as power sources for electric automobiles, storage of energy generated during intervals off-peak power consumption and various other applications. It is particularly applicable to current collectors for electrochemical cells that employ metal sulfides as positive electrode active materials and is particularly useful with electrochemical cells that have a positive electrode containing an iron sulfide as an active material.
The type of electrochemical cells contemplated are those that include the metal sulfides as the positive electrode reactant while the negative electrodes may include lithium in the form of solid alloys such as lithium aluminum alloys. These cells employ molten salt electrolytes generally including the halides of the alkali metals and possibly the alkali metal earths. A combination of individual salts permits reduced melting points and lower operating temperatures, and examples of these types of cells are well known in the art.
Current collectors in the forms of thin sheets, meshes, fiber compacts and the like have long been used to decrease the electrode resistance. Ideally, an electrochemical cell must maintain high power performance for the entire range of the state of charge. However in practice, a cell shows declining power characteristics as the discharge progresses due to increasing cell resistance. Some cells show more rapidly rising cell resistance than others, thus lowering specific power even where the weight of the current collectors are similar. Such difference of cell resistance comes partly from the difference in the current distribution in the electrode plates containing different current collectors. If a poorly conducting current collector is used in an electrode, the results are not only high cell resistant but also a subsequent rapid rise in cell resistance due to poor current distribution, which results in non-uniform utilization of the cell active material. Accordingly, it is important to design a current collector which gives low cell resistance as well as uniform current distribution.